In a disc recording/reproducing apparatus for recording or reproducing data on or from a disc-shaped recording medium, such as a CD player for reproducing a compact disc, the compact disc or the disc-shaped recording medium is rotationally driven at a constant linear velocity (CLV) by a spindle motor, and a laser beam is irradiated along a track formed spirally on the disc-shaped recording medium, so that a music program (digital data) recording as rows of pits on the track are reproduced by detecting changes in intensity of the reflected light which are caused by the presence or absence of the pits.
On the other hand, the bit error rate at the time of data reproduction in a CD player may reach an order of 10.sup.-5.
Since an error detection code and an error correction code are employed for correcting errors to a more or less extent, no inconveniences may arise under ordinary operating environments.
However, in a car-laden CD player or a portable CD player, extremely large vibrations may be produced, in a manner different from a stationary type domestic CD player, such that servo control may fall into disorder (deservoeing) due to an optical head scanning a disc track deviating from the track (or being off-track) to interfere with normal data reproduction. In such case, a music program cannot be reproduced satisfactorily because error correction cannot be made or reproduction may be interrupted even with the aid of the error detection code and the error correction code.
Thus, in a disc reproducing apparatus, such as a CD player or video disc player, should the reproducing head be off-track due to vibrations or the like, a problem is presented that reproduction of a continuous information of a music program, video program or the like is interrupted.
For overcoming the problem, there is known a method comprising providing a large capacity buffer memory, transiently storing data reproduced by a reproducing head, such as music program data, in the buffer memory, and outputting the data stored in the buffer memory as playback data even when the reproducing head is off-track for continuously reproducing the music program. However, with this method, it is necessary to store data previously in the buffer memory prior to reproduction of the music program, so that music program reproduction cannot be started immediately. On the other hand, an increase in buffer memory capacity is prohibitive.
With a disc recording apparatus such as a magnetic disc apparatus, a write-once type optical disc apparatus or an overwrite type optical disc apparatus, data recording is discontinued when the magnetic head is off-track due to vibrations or the like, so that continuously supplied input data cannot be recorded.
In view of the above described status of the art, it is an object of the present invention to provide a data reproducing apparatus in which continuous data may be reproduced even when the reproducing head is off-track.
It is another object of the present invention to provide a disc recording apparatus in which continuously supplied data may be recorded correctly even when the recording head is off-track.